Acoustic devices using amorphous metal alloys

ABSTRACT

Amorphous metal alloys are employed in acoustic devices dependent upon the properties of low acoustic velocity and low attenuation. Such devices include wire, strip and bulk delay lines.

United State: 2: f

Dutoit 1 Sept. 24, 1974 [54] ACOUSTIC DEVICES USING AMORPHOUS 2,672,590 3/1964 McSkimin.. 3'33/72 X METAL ALLOYS 2,700,738 1/1955 Havens 310/8.3 3,403,271 9/1968 Lobdell et al 310/83 X [75] Inventor: Michel Dutoit, Parsippany, NJ. [73] Assignee: $11k]?! (IEIh\e(mical Corporation, New Primary ExamineFJames W Lawrence or Assistant Examiner-Marvin Nussbaum [22] Filed: Feb. 5, 1973 Altorney, Agent, or Firm-Arthur J. Plantamura [21] Appl. No.: 329,935

7 ABSTRA T [52] US. Cl. 333/30 R, 310/83, 333/72 [5 1 C [51] I111. Cl. 03h 9/30, H01v 7/02 Amorphous metal alloys are employed i acoustic [58] Fleld of Search 333/30 R, 72; 310/83 i dependent upon the properties of low acoustic velocity and low attenuation. Such devices include [56] References C'ted wire, strip and bulk delay lines.

UNITED STATES PATENTS 2,503,831 4/1950 Mason 333/30 R 12 Claims, 1 Drawing Figure ACOUSTIC TRANSDUCER TRANSMITTING TRANSDUCER MEDIUM PATENIEUSEPEWH I 3.838.355

ACOUSTIC TRANSDUCER TRANSMITTING TRANSDUCER MEDIUM BACKGROUND OF THE INVENTION This invention relates to materials manifesting qualities of low sound velocity and low attenuation at high frequencies and to their use in acoustic devices which are dependent upon these specific qualities.

The present invention relates to the use of amorphous metals in acoustic devices, particularly guided wave devices such as wire and strip delay lines.

An acoustic delay line typically consists of a delay medium with one electromechanical transducer at each end. E.g., these transducers may be piezoelectric or magnetostrictive. One transducer launches an elastic wave which propagates down the delay medium and is then reconverted by the second transducer into electromagnetic form.

A key advantage of acoustic devices for signal pro-- cessing is their small size. This can be easily understood by considering the fact that the velocity of sound in solids is l0l0 times slower than the speed of light. If the signals are converted from electromagnetic waves, which travel at the speed of light, to acoustic waves of the same frequency, the same delay time can be obtained using an acoustic delay line correspondingly shorter than the coaxial cable needed to delay the signal in its electromagnetic form.

Since the discovery that certain materials exhibit very low absorption of acoustic energy at high frequencies, solid ultrasonic delay lines have been built-for dynamic storage of a great variety of signals. Various types of acoustic delay devices are in current use in communications, radar and computer systems.

Acoustic devices have a finite useful bandwidth determined by the transducers, the device dimensions and the loss in the delay medium.

Moreover, there are a number of factors which affect the amount of loss in the delay medium itself. Phononphonon interactions are generally responsible for most of the losses. For the purposes of this disclosure, we will consider two types of phonons: thermal phonons which are inherent in any solid and low frequency acoustic phonons injected by external means into the solid. At room temperature, thermal phonon lifetimesare much shorter than the period of the acoustic wave so that the rate of loss depends on how fast the disturbance of the thermal phonon population created by the propagating wave relaxes. A similar mechanism explains thermal conductivity. These two physical properties are closely related. Many dielectric crystals have been discovered that have low thermal conductivity and low attenuation. Glasses are known to have lower thermal conductivity than crystals of the same compositin. Indeed, in glasses there are many vibrational modes that scatter thermal phonons causing them to relax rapidly. It might then be deduced that glasses would show a lower attenuation at room temperature and would be ideal lowloss materials. This, however, has not been observed. Whereas the fast relaxation of disturbances in the thermal phonon distribution caused by the acoustic wave is indeed required for low-loss material, this seems to entail a strong direct interaction between acoustic phonons and thermal phonons and hence a large attenuation.

An additional absorption loss in delay media composed of polycrystalline metals is largely determined by grain size and sound wavelength. It has been found that the attenuation for plane waves in an infinite polycrystalline medium as a function of frequency may be expressed as af bf where a is the attenuation in dB/cm, f is the frequency, a and b are constants. The first term (af) expresses hysteresis losses and the second term (11)) is related to the grain structure of the material. Above a frequency of a few megahertz, the second term becomes dominant in most materials, limiting the bandwidth.

It will be realized that an ideal delay medium would comprise a material having low loss due to rapid relaxation of thermal phonons and minimal interaction between acoustic and thermal phonons as well as minimal absorption losses due to structural factors such as polycrystallinity.

For the purpose of this disclosure, two types of acoustic delay devices should be distinguished: 1) Delay lines using material with large lateral dimensions, sometimes also called bulk wave devices and 2) guided wave devices which use a delay medium confined in at least one lateral dimension to a fraction of an acoustic wavelength. In the first case, the elastic wave propagates essentially as a plane wave and is not affected by the lateral boundaries. In the second case, the wave strongly interacts with the lateral surfaces and propagates as a guided mode. Guided-wave delay devices are discussed extensively by J. E. May, Jr. in Physical Acoustics ed. by W. P. Mason, Vol. 1A p. 418 (1964), published by Academic.

The devices currently used for long delays at high frequencies include wire and strip delay lines.

Wire delay lines are used to store information for such purposes as a refresher for cathode-ray-tube alphanumeric displays and as a buffer unit between tape and magnetic core units in computers, for example. Because it is non-dispersive, the torsional mode of sound propagation is employed in these units. Filaments used in these delay lines are typically 1-50 mils in diameter, with a cross-section uniform to 1 percent and lengths from 10-100 feet. The majority of wire delay lines presently used employ ferromagnetic wires, particularly Fe-Ni alloys, which can be tailored to provide near zero temperature coefficient of delay. In order to get milliseconds of delay, it is necessary to use long (several feet) wires which are coiledinto flat spirals to provide more compact structures.

The chief disadvantage in the use of the polycrystalline wire is its large attenuation. As discussed above, losses are due mainly to scattering at grain boundaries and increase as the fourth power of frequency, thereby limiting the frequencies which can be used. Also, multiple reflections of the scattered beams produce a trailing hash on the end of the received pulse which limits the signal-to-noise ratio. Present delay lines have delays of 1-10 milliseconds and operate up to frequencies of only 2 MHz due to the acoustic losses of the wire.

Strip delay lines are used for similar applications as wire delay lines. They are made of metal strips, typically 20 mils thick, 1.5 in. wide and in. long. Aluminum is commonly used in these, but it has a high temperature coefficient. Acoustic losses limit the frequency range to 5-6 MHz with an attenuation of about 4 dB for a delay of l msec. Recently steels have been employed. However. they still exhibit the problems of polycrystalline structure.

At very high frequencies and above, bulk wave delay lines are used. Materials presently employed in these delay lines include oxide crystals, zero-temperaturecoefticient glass and fused quartz since they have low attenuation and can be cut to provide low temperature coefficients of velocities. However. they are fragile. particularly when cut into thin plates. and the oxide crystals are difficult to obtain in large enough pieces. For this application, strong materials with large lateral dimensions are needed.

SUMMARY OF THE INVENTION It is obvious that there is a need for acoustic materials which can be produced in long filaments or in bulk dimensions which possess low attenuation, low velocity, as well as mechanical strength and flexibility. The invention has an object to produce such materials for use in acoustic devices.

More specifically. it is an object of this invention to provide materials with the above-mentioned properties which can he used in wire or strip form in delay lines.

It is a further object to provide materials which can be used in bulk form for delay. devices employed in the VHF range.

Additional objects and advantages will become apparent from the description and examples provided.

In accordance with the invention, it has been discovered that the properties of glassy metal alloys, including their low ultrasonic attenuation. low sound velocity, reproducible acoustic and mechanical quality, the ability to be fabricated into long wires, strips and bulk quantities and their potential low cost, combine to make these materials uniquely suited for use in acoustic devices. The low attenuation may be due in part to the fact that, in contrast to the glasses discussed previously,.these glassy metals exhibit rapid relaxation of thermal phonons and minimal interaction between acoustic and thermal phonons. In addition, by the nature of the amorphous structure, there is no scattering at grain boundaries. These properties enable the amorphous metal alloys to be used in delay devices operating at higher frequencies, over wider bandwidths and providing longer delay times than any devices now available.

In determining the advantageous characteristics pursuant to the invention, the attenuation and velocity of sound have been measured for a variety of amorphous alloys. In performing these measurements, amorphous metal rods 10 mm long with diameters 1-2.5 mm were fabricated and thoroughly polished. Then piezoelectric transducers were bonded to these glassy metal rods and measurements between 50 and 500 MHz were performed. The results for the amorphous alloy Pd Ag Si are summarized in Table I together with results for the materials presently used for delay lines in each particular mode. Velocities are significantly lower than for conventional materials. It is also noted that the attenuation increases approximately as the square of frequency for the amorphous materials versus 1 for currently used polycrystalline materials. HEnce, at higher frequencies the advantages of the amorphous metals are even more apparent. v I

The compositions employed in the scope of this invention include any metals which can be produced in amorphous form, particularly those compounds represented by the general formula wherein T is a transition metal or mixture of said transition metals and X is an element selected from the group consisting of aluminum, antioony, beryllium, boron,

fgermanium, carbon, indium, phosphorus, silicon and tin and mixtures thereof and wherein the proportion in atomic percentages as represented by i and j are re- Table I Maximum (MHz) frequency Most Attenuation for l msec. Common Velocity (dB/msec. delay and IOdB Material Mode Use (l0 cm/sec) at 1 MHz) attenuation Amorphous longitudinal bulk delay 4.42 0.005 45 11.s ra.s Be lines Fused quartz longitudinal bulk delay 6.20 0.006 40 lines Amorphous shear strip delay 1.70 0.010 33 11.s 1e.s g i lines Polycrystalline shear "'srasaia 3.10 0.200 7 Aluminum lines Amorphous torsional wire delay 1.70 0.0l0 33 11.s to.s ge lines Polycrystalline torsional wire delay 3.00 2.000 2 Iron Nickel lines alloy Note: In comparing these materials it should be remembered that in polycrystalline materials the attenuation varies as f, in the amorphous metals as I.

lanthanum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, technetium, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, silver, and gold; preferably Fe, Ni, Co, V, Cr, Pd, Pt, and Ti. These materials are further characterized in co-pending US. application Ser. No. 318,146, entitled Novel Amorphous Metals and Amorphous Metal Articles.

Specific amorphous alloys exhibiting the desired properties include:

Fe P C B Si Al zo ss u s s m qo zo 'vs m s a Pd Cu Si so zo These amorphous alloys, in addition to having excellent acoustic properties have very desirable mechanical properties. For example, high tensile strengths and a high elastic limit as well as good corrosion resistance and unique magnetic properties are present in various selected compositions. Some are so ductile they can be bent over a radius of curvature less than their thickness and can be cut with a scissor. Also, with these ductile samples, tensile strengths of up to 350,000 psi have been obtained.

Further, it has been found that variousmetal alloys of the formula T x considered above have desirable properties of high strength and hardness, ductility and corrosion resistance even when they are partially crystalline 50 percent amorphous). Such materials are also considered here. It will be understood that for delay lines employing these partially crystalline metals, i.e., which is at least 50 percent amorphous metal alloy, the acoustic benefits which the amorphous structure imparts to the line will increase as the crystalline content decreases.

The amorphous metal wires may be prepared using any suitable technique which cools the molten jet sufficiently fast to avoid crystallization or jet breakup. The simplest such method is to squirt the molten metal stream into a suitably chosen liquid such as water or iced brine. An advantageous technique is that described in the co-pending application of S. Kavesh, Ser. No. 306,472, filed 11/14/72 in which the molten jet is quenched in a concurrently flowing stream of liquid. Any other processes which provide appropriate quenching conditions may be utilized, such as the processes described by R. D. Schile in U.S. Pat. Nos. 3,461,943 and 3,543,83l, in which the cooling of the molten jet through corona discharge, gas jets, and/or the deposition on the stream of a colder substance are used.

Illustrative examples of procedures which can be used to make amorphous metal strips are the rotating double rolls described by H. S. Chen and C. E. Miller, Rev. Sci. Instrum. 41, 1237 (1970) and the rotating cylinder technique described by R. Pond, Jr. and R. Maddin, Trans, Met. Soc., AIME 245, 2475 (I969).

Bulk samples can be prepared by drawing a fused silica tube to provide appropriate interior dimensions (typically with a mils diameter) and with thin walls to allow rapid heat transfer. Then the alloy is melted in the tube and rapidly immersed in a eutectic aqueous sodium chloride solution at -20C to quench the alloy in the glassy state.

In selecting any amorphous alloy, it should be noted that the specific characteristics of the material used in these acoustic devices vary accordingly to the use of the delay line. It is thus advantageous that these glassy metal alloys can be obtained for a wide range of constituents and compositions. The specific characteristics can be tailored to fit a given application. Essential properties for the objects of this invention are low acoustic loss, low temperature coefficient of sound velocity and good mechanical properties. In addition, magnetic properties are important in magnetostrictive delay lines.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE shows an exemplary acoustic device with which the amorphous metallic alloy of the present invention may be used.

PREFERRED EMBODIMENT OF THE INVENTION Generally, this invention is directed to the use of amorphous metal alloys in acoustic devices which depend for their efficiency upon low sound velocity and low acoustic attenuation. Such devices include wire and strip delay lines with center frequencies below 100 MHz and bulk delay lines operating in the VHF range.

Wire delay lines would be fabricated from wires ranging in diameter from about 1 to 20 mils, preferably from 4-8 mils. The choice of alloys would depend upon the requirements of the particular line. For general use, alloys of Pd NhSi Ni., I*"e P .,B Si A1 or Fe Ni cr P B Al would be satisfactory. They could be produced in any of the manners previously described for forming filaments. These wire delay lines would generally operate in a torsional mode, exhibit low attenuation and would be capable of producing delays of up to 10 msec at 10 MHZ with shorter delays at higher frequencies.

The strip delay lines of the invention may be prepared from amorphous metal strips ranging in width from about rt-2 in. and in thickness from about l-20 mils and generally operate in a shear mode. The exact composition selected depends upon usage but generally amorphous alloys of Pd,-, =,Ag Si, Ni, Cr P, B Si or Fe P C Al Si, are satisfactory and may be easily produced by known methods. The use of these metal strips in lengths of about 40 ft in the body of a delay line produces low attenuation and delays of up to 10 msec at 10 MHz, with shorter delays at higher frequencies.

Additionally, bulk delay lines may be produced from bars of the amorphous metals with highly polished ends from about 50-150 mils in diameter and from about Agin. in length. These bars provide low attenuation and up to 100 psec delays at frequencies of 100 MHz.

The body of these bulk lines may be composed of a variety of amorphous metal alloys produced in a size specification required. Included in this group of metal alloys are Pd Cu Si and Pd Ni Si for example.

It should be noted also that when considering the attenuation of these amorphous metals as compared with the polycrystalline metals presently used, that the attenuation of the amorphous alloys varies as f, while that of the polycrystalline alloys varies asf, so for high frequency applications, there is a very substantial difference in attenuation.

In conjunction with these forms of delay media, a variety of means for introducing an elastic wave into the media could be applied. Preferably, these means would be piezoelectric or magnetostrictive transducers.

The invention will be further described by the following specific examples. It will be understood. however, that although these examples may describe in detail certain preferred operating variables within the scope of the invention, they are provided primarily for purposes of illustration and the invention in its broadest aspects is not limited thereto.

EXAMPLE 1 A glassy Pd Ag Si wire was fabricated using the technique described in co-pending application Ser. No. 306,472 noted above. The alloy was melted in an argon atmosphere at 870C and extruded through a 12 mil orifice. The molten jet was quenched in a refrigerated brine solution at 20C. Brine velocity in the standpipe was 195 cm/sec. A continuous, smooth amorphous wire of round cross-section with a diameter of about mils was obtained. The amorphous nature of the wire product was confirmed by x-ray diffraction. The wire has an elastic limit of about 160,000 psi and a tensile strength of about 230,000 psi which is about 1/50 of the Youngs modulus for this glass, a value which approaches the theoretical strength of this material.

The amorphous wire product was cut to a length of 50 ft. Torsional mode piezoelectric transducers were fastened to both ends. The wire was coiled into a spiral 5 in. in diameter and fastened onto a board taking care that the supports did not dampen the signal. The whole assembly was enclosed in a case and flushed with dry nitrogen and sealed to avoid environmental changes. The delay line provided approximately 10 msec delay at 10 MHz with a total loss of about dB. In comparison the NiFe alloys presently used in delay lines give delays of 10 msec at frequencies of only 2 MHz.

EXAMPLE 2 Using the procedure of Example 1, an amorphous wire of Fe P C Al was prepared. A magnetostrictive delay line was made from this wire. A transducer coil was wound around a section of the wire near one end and the biasing field was applied by a permanent magnet. The transducer can be made movable along the wire to adjust the delay. Another transducer was placed near the other end of the wire to pick up the delayed signal. The wire was firmly mounted on a board, the assembly enclosed in a case, flushed with dry nitrogen and sealed. This delay line gave results comparable to those of the amorphous metal line element of Example EXAMPLE 3 Using the procedure of Example 1, amorphous wires of the following alloys were prepared.

ao zn zs n s z ss ss u s z w w m Ni Fe P B Si Al 11.s gs 1s.5

Pd NnSi so zo Measurements of the torsional mode of these wires gave velocities of less than 2.5 X 10 cm/sec and attenuations of less than 0.05 dB/msec at 1 MHz; values well below those of polycrystalline FeNi commonly used in wire delay lines and having a velocity of 3.0 X 10 cm/sec and attenuation of 2 dB/msec at 1 MHz. The maximum frequency for l msec delay and 10 dB attenuation for each of these amorphous compounds was greater than 25 MHz compared with 2 MHz for FeNi giving clear indication that delay lines using amorphous compositions are superior to those of presently used compositions with polycrystalline structure.

EXAMPLE 4 The alloy Fe Ni P B Al was placed in a fused silica tube with a 0.012 in. diameter hole in the bottom and melted at 1100C. The molten alloy was directed into the nip of the rotating double rolls, held at room temperature, described by Chen and Miller in Rev. Sci. Instrum. 41, 1237 (1970). The rolls were rotating at 1500 rpm. The quenched metal was entirely amorphous as determined by x-ray diffraction measurements, was ductile to bending and exhibited tensile strengths to 350,000 psi. A strip delay line was formed from a 15 ft length of this amorphous strip which was coiled on a 24 in. square plate and piezoelectric ceramic transducers were bonded to the ends to cause the excitation of the shear mode. Using this delay line, a delay of 4.2 msec was obtained at 8 MHz. A comparable delay time would require a strip of aluminum approximately 30 ft long and this would operate at a maximum frequency of only 2 MHz.

EXAMPLE 5 Following the procedure of Example 4, amorphous strips suitable for forming strip delay lines were prepared from the following alloys:

ao m 'zs n s z n rs s i ls ss m s q rs u s s 17.5 g6 is.s

su zo Acoustic measurements of the shear mode were made and all these amorphous strips were found to have velocities of less than 2.5 X 10 cm/sec, attenuation less than 0.05 dB/msec at l MHz, and could operate at greater than 25 MHZ maximum frequency with l msec delay and dB attenuation. These compounds therefore are superior to the present polycrystalline aluminum strips currently used in delay lines and which have a velocity of 3.1 X 10 cm/sec, attenuation of 0.2 dB/msec, and maximum frequency of 7 MHz for l msec delay and 10 dB attenuation.

EXAMPLE 6 A bulk rod of amorphous ld ,-,Ag Si, /z in. long and /8 in. in diameter was prepared by melting the crystalline alloy of the same composition to above 870C in a fused silica tube of approximately 100 mils diameter. The tube containing the molten alloy was then rapidly immersed in a eutectic aqueous sodium chloride solution at C to quench. After removal of the silica tube, the bulk rod was verified by x-ray analysis to be completely amorphous. The rod was then used in the body of a bulk delay line. Using this device, it was possible to obtain delays of up to 100 usec at 100 MHz.

I claim:

1. An acoustic delay device comprising in combination, a solid transmitting medium, a transducer for introducing elastic sound waves into said medium and a second transducer for reconverting said waves from said medium into electromagnetic form; said transmitting medium comprising a metal body which is at least 50 percent amorphous metal alloy.

2. The acoustic delay device of claim 1 in which the body is an amorphous metal alloy of the general formula wherein T is a transition metal or mixture of said transition metals and X is an element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, and mixtures thereof, and wherein the proportion in atomic percentages as represented by i and j are respectively from about to about 87 and from about 13 to about 30 with the proviso that i plus j equals 100.

3. The acoustic delay device of claim 2 in which at least one element of T is selected from the group consisting of Pd, Fe and Ni.

4. The acoustic delay device of claim 2 in which at least one element of X is selected from the group consisting of Si and P. i i 5. The acoustic delay device of claim 2 in which T is a combination of Pd and a member of the group consisting of Ag, Ni and Cu.

6. The acoustic delay device of claim 5 in which X is Si.

7. The acoustic delay device of claim 4 in which the amorphous alloy is Pd Ag Si 8. The acoustic delay device of claim 2 in which at least one element of T is a combination of Fe and Ni.

9. The acoustic delay device of claim 8 in which the amorphous alloy is Fe Ni P B Al 10. The acoustic delay device of claim 1 in which the body is in the form of a wire.

11. The acoustic delay device of claim 1 in which the body is in the form of a strip.

12. The acoustic delay device of claim 1 in which the body is in bulk form. 

2. The acoustic delay device of claim 1 in which the body is an amorphous metal alloy of the general formula TiXj wherein T is a transition metal or mixture of said transition metals and X is an element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, and mixtures thereof, and wherein the proportion in atomic percentages as represented by i and j are respectively from about 70 to about 87 and from about 13 to about 30 with the proviso that i plus j equals
 100. 3. The acoustic delay device of claim 2 in which at least one element of T is selected from the group consisting of Pd, Fe and Ni.
 4. The acoustic delay device of claim 2 in which at least one element of X is selected from the group consisting of Si and P.
 5. The acoustic delay device of claim 2 in which T is a combination of Pd and a member of the group consisting of Ag, Ni and Cu.
 6. The acoustic delay device of claim 5 in which X is Si.
 7. The acoustic delay device of claim 4 in which the amorphous alloy is Pd77.5Ag6Si16.5
 8. The acoustic delay device of claim 2 in which at least one element of T is a combination of Fe and Ni.
 9. The acoustic delay device of claim 8 in which the amorphous alloy is Fe35Ni42P14B6Al3.
 10. The acoustic delay device of claim 1 in which the body is in the form of a wire.
 11. The acoustic delay device of claim 1 in which the body is in the form of a strip.
 12. The acoustic delay device of claim 1 in which the body is in bulk form. 